SMH-A0304: Helmet Clamp Kit - For Ear buds with Attachable Boom Microphone & Wired Microphone. For the rider who has moulded ear plugs with speakers who has either a FULL FACE helmet and does not need a BOOM mic, or has an awkward helmet fitting (ie a Shuberth C2) for example. You retain the main Sena Bluetooth Unit.